Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation with a shaped charge perforating apparatus, as an example.
After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path through which fluids from the formation may be produced to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation.
Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. Specifically, one or more charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or other conveyance. Once the charge carriers are properly positioned in the wellbore such that shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, each shaped charge creates a jet that blasts through a scallop or recess in the carrier. Each jet creates a hydraulic opening through the casing and the cement and enters the formation forming a perforation.
When the shaped charges are detonated, numerous metal fragments are created due to, among other things, the disintegration of the metal cases of the shaped charges. These fragments often fall out or are blown out of the holes created in the carrier. As such, these fragments become debris that is left behind in the wellbore. It has been found that this debris can obstruct production as well as the passage of tools through the casing during subsequent operations. This is particularly problematic in the long production zones that are perforated in horizontal wells as the debris simply piles up on the lower side of such wells.
A need has therefore arisen for an apparatus and method that reduce the likelihood that debris will be left in the well following perforation. A need has also arisen for such an apparatus and method that will minimize fragmentation of the charge cases following shaped charge detonation. Further, a need has arisen for such an apparatus and method that will enhance the performance of the shaped charges.